Understanding Breath Test Reliability and the Observation Period
Overview
Breath test results often appear straightforward, but the reliability of the numbers depends heavily on proper procedure. The observation period, officer compliance, equipment handling, and environmental factors all influence whether the recorded result reflects true deep lung air.
Defense attorneys frequently rely on Zach Marshall to break down the technical steps behind breath testing, identify deviations from required procedure, and explain how those deviations affect the reliability of the final reading. As a DUI and collision consultant based in Arlington, WA, Zachary Marshall provides clear evaluations designed to support litigation, negotiation, and administrative hearings.
Why the Observation Period Matters
The observation period is one of the most misunderstood components of the breath testing process. Its purpose is to ensure that no mouth alcohol or foreign substances interfere with the sample.
A proper observation period requires:
Continuous, uninterrupted monitoring
No eating, smoking, or drinking
No burping, regurgitation, or vomiting
Officer attention at all times
An environment free from strong alcohol based contaminants
Gaps or distractions during this period can directly affect result reliability.
What Counts as “Observation”
Many officers believe that simply being in the same room satisfies the requirement. That is incorrect. Zach reviews:
Whether the officer had an unobstructed view
Whether they were actively watching the subject
Whether they were engaged in other tasks
Whether they left the room or turned their back
Whether video shows a loss of attention
Whether the officer documented observation accurately
Even small moments of inattention can undermine the validity of the reading.
Environmental Contamination
Breath tests can be influenced by the subject’s surroundings. Zachary evaluates potential contamination risks such as:
Alcohol based hand sanitizer
Cleaning agents
Mouthwash or hygiene products
Residual alcohol vapor in confined spaces
Equipment being cleaned nearby
Recent application of alcohol based products
These factors can distort the testing environment and reduce reliability.
Equipment Handling and Sequencing
Breath testing instruments rely on strict sequencing and handling. Zach examines:
Whether the machine was prepared properly
Timing of blank checks and air blanks
Whether the officer followed the correct prompt sequence
Any error messages or irregular readouts
Whether the second breath sample occurred within the required timeframe
Instrument status, calibration, and maintenance records
Incorrect sequencing or rushed steps can impact sample integrity.
Mouth Alcohol Concerns
Residual mouth alcohol is one of the most common causes of artificially high readings. Zach reviews:
Whether burping or regurgitation occurred
Whether the subject recently put anything in their mouth
If the officer documented any such events
Whether the subject made jaw or swallowing movements
Whether the officer responded appropriately
Video is especially important here, because it often contradicts the written narrative.
Clarity of Officer Instructions
Breath tests depend on the subject understanding and following instructions. Zach evaluates:
How clearly the instructions were given
Whether the officer demonstrated the proper breath pattern
Whether the officer interrupted or rushed the subject
Whether the subject appeared confused or anxious
Instruction clarity can significantly affect the quality of the sample.
Timing, Sequencing, and Reliability
Breath test timing must follow specific requirements. Zachary reconstructs:
Observation period start and end times
Timing between the first and second sample
Unusual delays or interruptions
Whether the officer documented these steps in the correct order
Whether the timing is consistent across video and reports
These timing factors often become critical in administrative hearings.
Why Attorneys Use Technical Breath Test Analysis
Attorneys rely on Zach Marshall because his breath test evaluations:
Identify reliability issues
Clarify procedural errors
Strengthen suppression arguments
Improve negotiation leverage
Support DOL and DMV hearing strategy
Provide clear, technical language for cross examination
Distinguish true impairment from procedural flaws
His structured reviews are designed to assist both private and public defense counsel across Washington and the West Coast.
Contact
For breath test reliability analysis, DUI evaluation, or hearing support, contact:
Zachary Marshall
Founder and Lead Consultant
Legal Limit Consulting, LLC
Arlington, Washington
Phone: (425) 224 5149
Email: Z.Marshall@LegalLimitConsulting.com
Website: www.LegalLimitConsulting.com
